Note:

You Do NOT Need CFW For PSP Themes, Either Have A CFW or An OFW That Is Capable Of Having Custom Themes

Installing Theme

1.Get A PSP Theme, you can get some from the site or google them, they are always a .ptf file
Eg. WoW.ptf, COD.ptf, etc.

2.Connect Your PSP To Your Computer Using A USB Cable Or If You Computer Has A Memory Stick Duo Slot Just Slot It In

3.Once Connected, Go To PSP And Make A New File Called 'THEME' (if you already have a THEME folder do not make another one)

4.Put Your Theme, Eg. COD.ptf Into Your New Folder 'THEME'

5.Disconnect Your PSP From Your Computer

6.On Your PSP Go To:
Settings->Theme Settings->Theme
and the you should be able to see your themes you installed

7.Just Open Your Theme, The Same Way You Open/Change Themes

There You Have It A Custom Theme On Your PSP

Rep+ If You Find This Useful

Well, the THEME folder is supposed to be inside the PSP folder on your Memstick, other than that, nice tut.

lol thanks, but not all memory sticks have a theme folder

I know that, but the THEME folder should be located inside of the PSP folder

yes all memory sticks have them. its ms0:/PSP/THEME

if you buy your own memory stick from shops, it wouldnt give you a theme folder because its not formatted with the psp yet